Does Driver Side have most weight on tires?

I don't know why Toyota does not say to rotate cross-vehicle, but ...

In general, for all cars, for safety / stability reasons, you always want the best tires (with the most traction = tread depth) on the rear.

This is to prevent oversteer / spinning out. In the extreme case, consider driving on ice or hydroplaning, with your front tires bald. You'd skid in the direction you're going, unable to turn, but basically staying straight. That's called understeer. With your rear tires bald, you would be unstable, and likely to spin out. That is called oversteer. The spinning out is obviously far more dangerous, and that is why many professionals will not allow installation of new tires up front, with old tires in the rear. The big chains (at least) have written policies against it, surely mandated by their insurers or shareholders.

This presents a common dilemma on front wheel drive cars, where the wear on the front tires is almost always greater due to: weight distribution, steering wear, misalignment wear, and drive wear. So the fronts will typically wear a little faster, and then you come to rotate front to rear to balance it out, and are faced with the stability issue. Solution is to not let it get too far out of balance front-rear. Or for us in California, where it literally does not rain for 8 months in a row or more every year, you can safely run with tires as bald as you want (exaggerating a little).

And related to the tread depth affecting fore-aft traction balance and spin stability, tire pressure factors in as well. Like many people, wanting better gas mileage, I put a few extra psi in my tires, hoping it improves rolling resistance at the expense of some comfort or traction. But I make sure to keep the fore-aft difference in pressure the same. I believe spec is 2 psi higher in the front, and I maintain that difference. Slightly lower pressure in the rear will provide slightly better traction, maintaining stability.

Still going ... similarly, for AWD / 4WD vehicles, when you put chains on two tires during snow conditions, you always put them on the rear - for the exact same stability reason. For front wheel drive cars, you have no choice but to put them on the front, but it is not ideal from a stability standpoint.

 

Tire shop people always put new tires in the back, they all said to me. When I ask why, they said it will break in faster. The underlying truth is putting the new tires in the back will cause the front tires to wear out even faster so you'll revisit them quicker in need of new pair of tires for front wheel drive cars.

 

Everything I wrote is accurate, FYI. Not making anything up. For your benefit, please fact check on the goog if you don't believe it. When rules are formulated, they're considering the worst case. So they're trying to prevent the 1/100,000 case that you'd spin out when going through an unexpected puddle on the freeway. True, you probably would not notice anything during normal Prius-style driving.

And of course, yes, it would be best to not have any bald tires. But if you do, you want them on the front. Yes, balanced is best. If not balanced, you want more traction to the rear, for stability reasons. 4 new tires is better than two new tires in the rear and two bald ones in front. Check.

 

It's not a bad solution. Might save you from overthinking it.

 

For that extreme case, add in some bouncy uneven surface conditions while entering a corner, just as a panic braking circumstance suddenly emerges from around that corner. Then imagine all this in an old-fashioned non-ABS car. Bald rear tires almost guarantee a spinout, as the rear end continues moving on the slippery surface and goes ahead to become the new front end.

Worst case is then getting T-boned by an oncoming vehicle while part way through that spin. The side impact protection is far less effective than the head-on impact protection.

Today's ABS and stability controls do significantly improve the situation, but can't work miracles by creating traction out of thin air. Or rather, from ice or water sheets.

How do new tires on one end cause the older tires on the other end to wear out faster?

The emergency braking spinouts from large traction asymmetries, described above, are the real reason. Regular rotations are meant to keep any asymmetries small and more controllable.